The present invention relates to high current feeding for an electric arc, twin hearth furnace.
Electric smelting i.e. metallurgic furnaces, particularly arc furnaces, require the feeding of electric current to the electrodes. It has been the practice to run the conductors in partially suspended fashion from the transformer to the electrode sockets. A flexible connection is required because the electrodes are moved during the operation; particularly voltage changes require control operations which are effected by lowering or raising the electrodes, while the transformer connections remain stationary.
It is known that certain problems arise in the case of an uneven, i.e. unsymmetrical arrangement, of the three phase conductors. These problems are of a technical nature and are caused by the mutual electromagnetic interference of the conductors which run to the electrodes. In particular, during movement and displacement of the electrodes the conductors are moved accordingly, but not in unison, they therefore change their mutual position. Since this movement is not carried out in infinitisimally small steps but have a noticeable speed inductive forces are set up as between the several conductors which effectively increase the inductivity of the system as a whole and, therefore, increase the wattless power of the system. The increase in wattless power, of course, has to be covered by an increase supply of energy.
In order to match the different inductivies of the several conductors, i.e. in order to provide some form of equalization, it has been the practice to run the conductors in a so-called triangulated arrangement in order to make sure that they are mutual spacing and distance remains constant even when the electrodes are moved up or down. This has not been successfully practiced thus far. The overall problem is a twofold one: displacement of each conductor as such and a change in its geometrical configuration changes the inductance of the respective conductor path. However, any mutual position change among the conductors introduces asymmetry into the overall inductive behavior and that, ultimately, is reflected in local nonuniformities in the smelting process.
Steel smelting plants using several furnaces are sometimes provided with a common, pivotable cover or lid as is disclosed, for example, in German printed patent application No. 3102499. With regard to the requisite symmetry among the conductors, this kind of arrangement poses particular problems. The several conductors are not only displaced as such in dependence and during the adjustment of the elevation of the electrodes, but they also change their position in relation to each other upon pivoting the electrode arc. Therefore, the known rigid conductor system, as is for example disclosed in German printed patent application 3016087 is not suitable for that kind of furnace.